This invention relates to a multi-disc aircraft brake system and more particularly to a new and improved heat shield for an aircraft multi-disc friction braking system.
During the braking of an aircraft, the alternately splined stator and rotor discs of the multi-disc brakes are brought into sliding contact with each other, generating considerable heat energy that must be dissipated to eliminate the highly deteriorative effects on the wheel and tire structure which, in certain instances such as abortive or rejected take-off, can result in sufficiently high heat to result in tire fires.
As the heat, heat energy or brake energy is generated within the braking elements of the stators and rotors (hereinafter also referred to as the heat sink), such heat energy is dissipated via conduction, radiation and convection to the adjacent braking components, such as the wheel assembly, bearings, pistons and other adjacent structures. It is important to limit the heat transfer to protect the structures as much as possible. One manner of protecting these areas is to provide a heat shield between the heat generating elements of the (stator and rotors) heat sink and the wheel assembly, with its adjacent components and bearings. Some heat shield constructions, as proposed and shown by U.S. Pat. Nos. 4,944,370 and 3,958,833, use a solid integral cylinder that prevents the transmission of heat energy directly radially outwardly from the heat sink with openings only at the respective axially-spaced ends. Such complete blocking of the heat energy transfer is not desirable, as this leads to heat concentration in the heat sink itself, which can lead to premature failure therein under heavy duty brake application, as in abortive take-offs. It is an object of the present invention to provide a heat shield that permits heat energy dissipation in a controlled, efficient manner without increasing the weight of the braking system. The present invention recognizes the need to provide a heat shield that can dissipate the heat energy from the heat sink radially, as well as axially. It is an object of the present invention to provide a heat shield that surrounds the heat sink and that allows controlled radial dissipation of heat energy by radiation, while simultaneously encouraging the dissipation of heat energy by convection, without concentrating the build-up of heat energy at the heat sink itself. Convection is defined as the transfer of heat by a circulatory motion through a medium at a non-uniform temperature, owing to the variation of density and the action of gravity. In this process, there must be a medium through which this heat transfer process occurs. In the case of the transfer of heat energy by radiation, the energy travels as a wave motion, which requires no medium for such transfer. Thus, in the case of two surfaces in space with no medium (such as air) between them, there can be a transfer of heat energy between them only by radiation and not by convection. Further, a necessary condition for two surfaces to transfer radiation energy to each other is that the two surfaces must be able to "see" or "view" each other, the magnitude of the radiation exchange between the two surfaces is directly proportional to how much of each surface is "visible" to the other surface. For example, if the two surfaces in space had a plate between them with a small hole therein, then the transfer of heat energy by radiation would be reduced to that only transmitted by the line of sight along lines interconnecting the two surfaces through the small hole in the plate. If such plate with the same diameter hole were made substantially thicker, then the amount of heat energy transferred would be reduced, since the deeper hole with the cylindrical wall would reduce the area exposed for transfer and emission of the heat energy.